1. Field of the Invention
This invention relates to the field of refrigeration, and more particularly relates to a pneumatic system which provides efficient cooling without the use of environmentally-harmful refrigerants.
2. Description of the Related Art
A common refrigeration technique is based on the principal that rapidly expanding a pressurized refrigerant gas initially at or near ambient temperature cools the refrigerant. Preferably, the refrigerant gas is expanded sufficiently rapidly to liquify the refrigerant so that the refrigerant absorbs an additional quantity of heat in re-evaporating. One drawback to such systems is that commonly used refrigerants such as fluorocarbons and ammonia are frequently toxic or react to form environmentally-harmful compounds if released or vented to the atmosphere. While environmentally-tolerable refrigerant compounds are available, such compounds tend to be relatively expensive and are often corrosive.
While air is more environmentally-friendly than such commonly-used refrigerants as ammonia and fluorocarbons, it is also less efficient. Indeed, air is a mixture of gases, and certain components such as carbon dioxide have very low boiling points and are difficult to liquefy in cryogenic systems. In addition, the air in a pneumatic refrigeration system may carry biological or chemical contaminants incompatible with sterile environments such as food storage areas. Oil droplets and water vapor entrained or evaporated into the air may collect on the inner surfaces of the system, particularly in cooler sections, and interfere with its operation. Consequently, there exists a need to inhibit airborne contamination from the air flow in a pneumatic refrigeration system and to increase the efficiency of such systems to offset the loss of efficiency inherent in the use of air rather than less environmentally-friendly but more efficient refrigerants.